Researchers use sampling in taking a census of the entire population is impractical. Data from the sample are used to calculate statistics, which are estimates of the corresponding population parameters. For instance, a sample might be drawn from the population mean, its mean is calculated, and this value is used as a statistic or an estimate for the population mean. Thus, descriptive measures computed from a population are called parameters while descriptive measures computed from a sample called statistics. We say that the sample mean is an estimate of the population mean μ.